JP2000079445A - Mold for continuously casting steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold for continuously casting steel so as not to generate a longitudinal crack, rhombic deformation etc., causing the deterioration of quality by promoting the generation of a solidified shell and uniformizing the thickness of the solidified shell. SOLUTION: Cross sectional shape in a mold main body part 1 of a mold for continuously casting is a quadrangle connecting four straight line sides with four of 1/4 circular arcs, the inner circumferential length is long at the upper end side of the mole main body part 1 and short at the lower end side and the reducing ratio of the inner circumferential length is reduced from the upper end toward the lower end of the mold main body part 1. This inner circumferential length is changed with only a tapered amt. in the mold main body part 1 or with the both of the tapered amt. and the radius of the 1/4 circular arc. This mold MD for continuously casting is used and the surface of molten steel is displaced in the vertical direction and a mold part having the approximately same inner circumferential length as shrunk outer shape at the initial stage of solidification of a cast billet is used so as to keep the contact state of the solidified shell with a mold copper plate to an optimum condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting mold for steel.

[0002]

2. Description of the Related Art Conventionally, continuous casting molds for rectangular cast slabs are roughly classified into those having a cross section similar to that of a product slab and those having at least a part having a deformed cross section, that is, a mold having a cross section having a cross section. Some products are not similar to product slabs. As for the mold having a cross section similar to that of the product cast piece, a mold having a single taper or a mold having a multi-stage taper in which a taper amount is divided into a plurality of steps in a casting direction and a taper amount is changed in each step is known. The basic casting method using this rectangular mold is to keep the molten steel level in the mold constant (generally around 100 mm below the top of the mold). In other words, although it may be artificially moved around 20 mm for the purpose of extending the life of the immersion nozzle and the copper plate, the basic idea is to maintain the specified target level as much as possible regardless of the increase or decrease in the casting speed. It is.

[0003] The mold having the irregular cross section is intended to increase the casting speed and prevent slab breakage and breakout, and is disclosed in Japanese Patent Application Laid-Open No. Hei 4-319044 and US Patent No. 4207941. There is. The mold described in Japanese Patent Laid-Open No. Hei 4-319044 has a mold 103 as shown in FIGS.
In the upper half, the four sides are curved and overhang and overhang 109
The overhang 110 is reduced downward, and the cavity 106 is formed in the lower half 113 of the mold in a substantially square shape. The mold described in U.S. Pat.No. 4,420,791 has an upper end 202 of the mold as shown in FIGS.
Is a quadrilateral having a valley-shaped corner, the middle portion 204 is tapered, and the lower end 206 is formed in a C-shape at the lower end portion 206, and is formed in an irregular dodecagon.

[0004]

However, in a conventional casting method using a mold having a cross section similar to that of a product slab, the setting of the molten steel level in the mold depends on operating conditions such as steel type, casting temperature and casting speed. Even if it changed, the cavity size in the mold was basically the same, so the slab was constrained in the mold even under the most critical operating conditions (ie, when casting steel with low shrinkage due to initial solidification at high speed). A small taper was used so that it would not occur. Therefore, under normal operating conditions, the contact area between the mold copper plate and the cast slab is limited to the entire circumference up to 200 to 300 mm below the level of molten steel in the mold, and below that, the contact area is limited to the center of each side. We had to operate under the condition.

[0005] In this case, the vicinity of the corner of the cross section of the slab cools faster than each side, and in the conventional mold, it separates from the copper plate immediately after the initial solidification, causing a delay in shell formation near the corner. . This forms a defective shell formation portion near the corner, hinders an increase in casting speed, and causes quality deterioration such as vertical cracking and rhombic deformation near the corner. On the other hand, if the cross-sectional shape is changed in the casting direction as in the case of a conventional mold having a modified cross section, it is difficult to manufacture, maintain and maintain the mold, and disadvantageous in terms of wear life. Further, there is a problem that the cross section of the cast slab is not a square but a dodecagon.

The present invention has been made in view of the above circumstances, and has a
Instead of using a deformed cross-section mold that is difficult to maintain, use a square-based mold to promote the formation of a solidified shell, make the solidified shell thickness uniform, and eliminate vertical cracks, rhombic deformation, etc. that cause quality deterioration. It is an object of the present invention to provide a mold for continuous casting of steel that is prevented from occurring.

[0007]

According to a first aspect of the present invention, there is provided a continuous casting mold, comprising: a mold body portion where molten metal poured into contact with a mold copper plate; and an upper end allowance where molten steel above does not contact the mold copper plate. Wherein the cross-sectional shape of the mold body is a quadrangle in which four straight sides are connected by four quarter-arcs, and the inner peripheral length is the upper end side of the mold body. , And is reduced at the lower end side, and the circumferential length of the mold main body portion is changed only by the taper amount of the mold main body portion.

According to a second aspect of the present invention, there is provided a continuous casting mold comprising: a casting body portion in which molten metal poured into contact with a casting copper plate; and an upper end margin portion in which molten steel above does not contact the casting copper plate. Wherein the cross-sectional shape of the mold body is a quadrangle in which four straight sides are connected by four quarter arcs, and the inner peripheral length is large at the upper end of the mold body and smaller at the lower end. The inner peripheral length of the mold main body portion varies depending on the taper amount of the mold main body portion and the radius of a quarter arc.

At the time of continuous casting, the shape of the shrunk slab and the shape of the cavity in the mold are well matched, and the smaller the air gap between the mold copper plate and the solidified shell, the more the contact between the solidified shell and the copper plate can be ensured. The formation of a solidified shell can be promoted. By the way, when observing the process of molten steel solidifying in the mold and forming a solidified shell,
It was found that the shrinkage was approximately 200 to 300 mm below the surface of the molten steel, and the subsequent shrinkage was not so large. It is also known that the degree of shrinkage during initial solidification greatly depends on operating conditions such as the type of steel, casting temperature, and casting speed.

Therefore, in the present invention, by intentionally changing the set level of the molten steel surface in response to changes in operating conditions, a mold portion having an inner peripheral length that is well matched to the shrinkage of initial solidification can be selectively formed. use. That is, by using a mold body portion having an inner peripheral length approximately equal to the contracted outer shape of the slab, the slab corner portion is formed by the action of pressing each side of the slab to the center side where each side of the copper plate is opposed. It prevents you from moving away from it. In addition, even if the operating conditions change and the contact between the initially solidified shell and the copper plate becomes excessive or insufficient, the optimal contact state can always be maintained by lowering and increasing the set level of the molten steel level in the mold. .

[0011]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view of a mold MD according to the present invention, wherein 1 is a mold main body portion where molten metal m poured into contact with a mold copper plate, and 2 is an upper end margin portion above it.
The upper end margin 2 is a part for preventing the outflow of molten steel at the time of pouring, and does not normally come into contact with molten steel m during operation. The molten steel m comes into contact with the mold body portion 1, and the upper end thereof is at a level where the molten steel m rises most during operation. The present invention is characterized by the setting of the inner peripheral length of the mold body 1.

The cross-sectional shape of the mold MD according to the present invention is a quadrangle, in which four straight sides are connected by four quarter-arcs. Note that the quadrangle in this specification includes a long quadrangle, and the ratio of the long side A to the short side B is A / B.
≦ 2.0 are included in the present invention. The inner peripheral length S of the cross-sectional shape in the present invention is larger at the upper end side of the mold main body portion 1 and smaller at the lower end side, and the inner peripheral length S may be changed only by the taper of the mold main body portion 1, It may be varied by both the taper and the radius of the quarter arc. When the taper amount is changed, it may be changed stepwise as shown on the left side of FIG. 1 or may be changed continuously as shown on the right side of FIG. When the taper amount is changed stepwise, the upper part 3 and the lower part 4 may be divided into two stages or three or more stages as illustrated on the left side of FIG. The taper of the upper end margin 2 may be arbitrarily attached irrespective of the mold body 1 or may not be attached.

The reduction rate of the inner peripheral length S defined by the amount of taper or the amount of taper and the radius of a quarter arc of a corner in the mold body portion must decrease from the upper end to the lower end. That is, it is characterized in that the degree of change of the inner circumference length is large at the upper end, and the degree of change is small at the lower end.

Next, the manner of changing the inner circumference S will be described in more detail with reference to FIGS. FIG. 2 is a schematic vertical sectional view of a mold main body, and 5 is a body plate. Generally, the body plate 5 is formed to be curved, but is simply and straightly drawn in this figure. 3A to 5A are cross-sectional views of the upper end, the central portion, and the lower end in FIG. 2, respectively, and FIG. 3B is an enlarged view of a corner arc portion.

As shown in FIG. 2, an origin 0 is set on the inner surface excluding the corners at the lower end of the mold, and the Y axis is set in the upward direction parallel to the casting direction of the mold, and the X axis is set in the direction perpendicular thereto. y =
The distance from 0 to the upper end of the mold main body portion is L (mm), and the opposite side dimension in an arbitrary cross section AA section (Y = y) is B
(Y), assuming that the radius of a quarter arc of the corner is R (y), the inner circumference S (y) is expressed by the following equation. S (y) = 4 ｛B (y) −2 · R (y)｝ + 2π · R (y) where B (y) = Bo + 2xx Since x is expressed as a function of y as described above, x = f
(Y), and the relationship between x and the taper is dS (y) since mold taper = 2 / Bo · dx / dy × 100.
/ Dy = 8 · dx / dy− (8−2π) · dR (y) / d
y.

Now, assuming that the mold taper is Tm, d
S (y) /dy=Bo/25.Tm- (8-2.pi.). DR
(y) / dy, and as is apparent from the above equation, the circumference S
Is the rate of change in the y direction of the taper Tm and the radius R of the corner arc.
Is a function of the rate of change dR (y) / dy. If the radius R of the corner arc is constant, dS (y) / dy = Bo
/ 25 · Tm, which is a function dependent only on the taper. Therefore, by changing the taper while keeping the radius of the taper and the radius of the corner arc or the radius of the corner arc constant, the inner peripheral length change rate S (y) of the cross section of the mold body 1 can be set arbitrarily.

However, if the rate of change of the inner circumference S (y) is too small, it is impossible to use a mold portion having an inner circumference approximately equal to the contracted outer shape of the slab, which is the object of the present invention. On the other hand, if it is too large, the slab is restrained and causes a breakout. Therefore, the inner circumference length change rate S (y) is 0 ≦
In the range of dS (y) /dy≦0.08, it is preferable that the ratio is large at the upper end of the mold body 1 and smaller at the lower end. The cross-sectional shapes shown in FIGS. 3 to 5 are examples in which the radius R of the corner arc changes from large to small from the upper end to the lower end of the mold body 1.

Next, a preferred example of the cavity size in the mold is shown as follows based on FIG. In addition,
The mold of the present invention is not limited to this. (1) Upper mold area (L-400 ≦ y ≦ L shown in FIG. 6 (A))
1.5 ≦ Tm ≦ 15 (% / m) 0 ≦ dR (y) /dy≦0.15 0.005 ≦ dS (y) /dy≦0.08 (2) Mold lower region (0 ≦ y ≦ L-150
0 ≦ Tm ≦ 5.0 0 ≦ dR (y) /dy≦0.030 0 ≦ dS (y) /dy≦0.025 (3) The above values are constant or increase as y increases. The upper margin 2 is 50 mm.

Next, a continuous casting method using the above mold will be described. In the present invention, by intentionally changing the set level of the molten steel surface in response to changes in operating conditions, a mold portion having an inner circumferential length S that matches well with the shrinkage of initial solidification is selectively used. Is the inner circumferential length S of the mold body 1
However, when using a mold MD that can be changed only by the taper Tm, using a mold body portion 1 having a circumference reduction rate approximately equal to the contracted outer shape of the slab, each slab of which the copper plate side faces each other The action of pushing the side toward the center is performed, thereby preventing the corner of the slab from coming off the copper plate 5.

When the mold MD in which the inner circumferential length S of the mold body 1 is changed by the taper Tm and the radius R of the corner arc is used, not only the reduction rate of the circumferential length S but also the cross section of the mold cavity is used. After a solidified shell having a large radius of curvature is initially formed at the corner arc, the radius of curvature is reduced toward the lower end of the mold, so that contact between the solidified shell and the copper plate at the corner is ensured.

Furthermore, even if the contact between the initially solidified shell and the copper plate is excessive or insufficient due to changes in operating conditions such as steel type, casting temperature, casting speed, etc., the set level of the molten steel level in the mold is lowered. The optimal contact state can be maintained by raising. The range of the rise and fall is preferably 10 to 200 mm below the upper margin 2 in FIG.

As described above, when the operating conditions such as the casting temperature and the type of steel change, the physical quantity representing the contact state between the solidified shell and the mold copper plate changes. By measuring or calculating these physical quantities, The molten steel level in the mold may be intentionally moved so that the value falls within an appropriate range. Examples of the physical quantity include (1) pull-out resistance in the mold, (2) copper plate temperature, (3) temperature difference between the supply side and the drain side of the mold cooling water, and the like. It can be an index.

For example, if excessive contact occurs during the operation, physical quantities such as the temperature difference between the inlet and the outlet of the mold cooling water, the temperature of the copper plate, and the resistance value of the pulling resistance in the mold increase. If this tendency further progresses, the tensile stress of the solidified shell below the slab constrained by the mold breaks beyond the allowable limit, leading to breakout. Therefore, when the values of these physical quantities exceed a predetermined range, it is preferable to lower the level of molten steel in the mold and use a mold portion having a small taper and a rate of change in inner circumference length. Conversely, when the contact between the copper plate and the solidified shell is small, the above physical quantity decreases. In this case, when the level of molten steel in the mold is increased, a portion having a large mold taper and a change rate of the circumferential length is used, and the physical quantity increases. Therefore, by operating while monitoring the above physical quantities,
Optimal contact can be maintained.

It should be noted that the physical quantity representing the contact state between the mold copper plate and the slab does not need to be measured each time casting is performed, but an appropriate calculation of the molten steel level in the mold with respect to the operating conditions is performed based on data accumulated in advance. It is also possible to establish a method.

Next, specific means for detecting the physical quantity will be described. FIG. 7 shows the oscillation device in a state where the mold MD is placed on the mold table 11, and as an example of detecting the pull-out resistance in the mold, a load meter 14 is installed between the push rod 12 and the eccentric rotator 13. Things. Thereby, the pull-out resistance in the mold can be detected. FIG. 8 shows thermocouples TC1 to TC6 on the back side (mold cooling water side) of mold copper plate 5.
Is embedded. It is to be noted that the apparatus using a thermocouple as the molten steel level detecting apparatus in the mold can be used also. The thermocouple embedded in the copper plate 5 can express the contact state between the mold copper plate 5 and the solidified shell more directly than the above physical quantity. FIG. 9 shows a cooling device for the mold MD. If the temperatures at the supply port 16 and the drain port 17 of the cooling water are measured, the temperature difference between the supply water temperature and the drain temperature can be used as a physical quantity.

[0026]

According to the present invention, by moving the molten steel level in the mold up and down, the contact between the mold copper plate and the slab can be optimized, so that the solidification of the slab drawn from the mold can be achieved. The shell is thicker and more uniform than before, and high-speed casting can be performed without fear of breakout, and rhombic deformation hardly occurs.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a continuous casting mold according to the present invention.

FIG. 2 is a view for explaining an inner peripheral length in a mold body portion of the mold according to the present invention.

3 (A) is a cross-sectional view of the upper end of the mold body in FIG. 2, and FIG. 3 (B) is an enlarged view of a corner arc.

4 (A) is a cross-sectional view of a central portion of a mold main body portion in FIG. 2, and FIG. 4 (B) is an enlarged view of a corner arc portion.

5A is a cross-sectional view of the lower end of the mold body in FIG. 2, and FIG. 5B is an enlarged view of a corner arc.

FIG. 6 is an explanatory view of an upper region and a lower region of a mold body in a continuous casting mold according to one embodiment of the present invention.

FIG. 7 is an explanatory diagram of an oscillation device provided with a pull-out resistance detector in a mold.

FIG. 8 is an explanatory diagram of a temperature detecting device for a mold copper plate.

FIG. 9 is an explanatory diagram of an apparatus for detecting a cooling water temperature of a mold.

FIG. 10 is a longitudinal sectional view of a mold according to a conventional example.

FIG. 11 is a plan view of the mold of FIG. 10;

FIG. 12 is a longitudinal sectional view of a mold according to another conventional example.

FIG. 13 is a plan view of the mold of FIG. 12.

[Explanation of symbols]

MD Mold m Molten steel 1 Mold main body 2 Margin at upper end S Inner circumference R Radius of corner arc

Claims (2)

[Claims] 1. A continuous casting mold comprising a mold body portion in which molten metal poured into contact with a mold copper plate and an upper end margin portion in which molten steel above does not contact with the mold copper plate, wherein the molten steel crosses the mold body portion. The surface shape is a rectangle in which four straight sides are connected by four quarter arcs, and the inner peripheral length is large at the upper end side of the mold main body portion and smaller at the lower end side, and the circle of the mold main body portion is A casting mold for continuous casting of steel, wherein a circumference of the casting mold is changed only by a taper amount of a casting body. 2. A continuous casting mold comprising a mold body portion in which molten metal poured into contact with a mold copper plate and an upper end margin portion in which molten steel above does not contact the mold copper plate, wherein the molten steel crosses the mold body portion. The surface shape is a quadrangle in which four straight sides are connected by four quarter arcs, and the inner peripheral length is large at the upper end side of the mold body portion and smaller at the lower end, and the inner periphery of the mold main body portion is A continuous casting mold for steel, wherein the length varies depending on a taper amount of a mold main body portion and a radius of a quarter arc.